World’s Soil Resources

Figure 15.1 Nations in the Southwest Pacific region and the extent of Melanesia, Micronesia and Polynesian cultures. Figure based on
base map imagery: exclusive economic zone boundaries (EEZ)v 8 2014, Natural Earth 11 3.2.0
Ancient landscapes
After separating from Antarctica, the Australasian landmass moved northwards into warmer latitudes at
the same time that the globe was cooling during the Pleistocene. The development of the circumpolar Southern
Ocean further moderated the climate of the Australasian landmass. The resulting relative stability meant
that biological evolution and soil development occurred on similar timescales and without major phases of
interruption. This is in contrast to much of the Northern Hemisphere where repeated glaciations renewed
landscapes and ensured that large areas have relatively young soils. This long history of soil development has
many implications today for land management in the region.
Low-relief landscapes of Australasia
The western two-thirds of the Australian continent are dominated by ancient landscapes and strongly
weathered soils. Some of these soils bear the imprint of previous climates with some unexpected patterns of
soil distribution – very acid leached soils (normally associated with humid regions) now occur in deserts, and
deeply weathered soil profiles (tens of metres deep) occur in Mediterranean climates with limited leaching.
Vast areas of sandy soils have formed from the predominantly acid-igneous and sedimentary parent materials.
Nutrient status is very poor and micronutrient deficiencies are common. In the south, substantial quantities
of salt have accumulated in the low relief landscapes. As a consequence, sodic and saline soils are widespread
and human-induced salinity is a major land management problem.
Uplifted and eroded continental margins
The soils and landscapes of the eastern third of Australia are dominated by the influence of the Great
Escarpment (Ollier, 1982) – a landscape feature that extends for 3 000 km from Northern Queensland to
Victoria. The Great Escarpment was formed by uplift associated with the passive continental margin to the
east. Inland of the Escarpment, the soils and landscapes tend to be older but more clay-rich than in the west
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in the Southwest Pacific